This study examines how culture shapes the understanding, diagnosis, support, and lived experiences of autistic individuals across different societies worldwide. Using a systematic review and qualitative synthesis design, the study analyses existing literature from Africa, Asia, Europe, the Americas, and Oceania, guided by the Communicative Reciprocity Theory of Behaviour and the Social Model of Disability. Findings reveal that autism is interpreted variously as a medical condition (Western countries), a spiritual phenomenon (many African communities), a family reflection (Asian cultures), or natural human variation (some Indigenous groups). These interpretations directly affect whether families seek clinical help, traditional healers, or no intervention. Diagnostic tools developed in Western contexts often misclassify culturally normative behaviours such as avoiding eye contact or speaking softly as symptoms, leading to widespread under-diagnosis in low- and middle-income countries and among ethnic minorities. Interventions focused on individual independence conflict with collectivist values in many societies, while stigma ranges from severe shame and concealment to acceptance and celebration depending on cultural attitudes toward family reputation and social harmony. Major research gaps persist, with most studies coming from wealthy Western nations. The study concludes that effective global support requires culturally responsive diagnostic tools, interventions that respect local communication styles and family structures, public education to reduce stigma, and policies co-designed with local communities. Recommendations are provided for policymakers, practitioners, researchers, international organisations, and families. Without fundamental changes to current Western-centric approaches, most autistic people worldwide will continue to be denied appropriate recognition, support, and opportunities to thrive.